BUTTSTOCKS:

Cole Components http://colecomponents.com/
Luth-ARs http://www.luth-ar.com

HANDGUARDS:

Hardened Arms http://www.hardenedarms.com/ecProductListing_58
ODIN Works https://www.odinworks.com/category_s/1904.htm?searching=Y&sort=2&cat=1904&show=10&page=2
OffHand Gear http://www.offhandgear.com/ar-15-hand-guards/
Unique-ARs https://unique-ars.com/product-category/hand-guards/
Radical Firearms http://www.radicalfirearms.com/category-s/1835.htm
Yankee Hill http://yhm.net/accessories/forearms.html
Midwest Industries https://www.midwestindustriesinc.com/category-s/329.htm
UTG Pro (not slim or super slim) http://leapers.com/search.php?criteria=MTU
Samson Mfg - Evolution http://www.samson-mfg.com/category/Evolution-Standard-Lengths.html

MAGAZINES:

AICS Magazine http://www.brownells.com/magazines/rifle-magazines/magazines/long-action-ax-5rd-magazine-338-lapua-prod71844.aspx?avs%7cCapacity_1=5-Round&avs%7cCartridge_1=DCC_338%2bLapua
Accurate Mag http://store.accurate-mag.com/sssf338lapuamagnum.aspx
Wyatt Outdoors http://wyattsoutdoor.com/product_info.php/cPath/2/products_id/49